Within the body of a healthy adult, microbial cells are estimated to outnumber human cells by a factor of ten to one. These communities, however, remain largely unstudied, leaving almost entirely unknown their influence upon human development, physiology, immunity, nutrition and health.
Traditional microbiology has focused on the study of individual species as isolated units. However many, if not most, have never been successfully isolated as viable specimens for analysis, presumably because their growth is dependent upon a specific microenvironment that has not been, or cannot be, reproduced experimentally. Among those species that have been isolated, analyses of genetic makeup, gene expression patterns, and metabolic physiologies have rarely extended to inter-species interactions or microbe-host interactions. Advances in DNA sequencing technologies have created a new field of research, called metagenomics, allowing comprehensive examination of microbial communities, even those comprised of uncultivable organisms. Instead of examining the genome of an individual bacterial strain that has been grown in a laboratory, the metagenomic approach allows analysis of genetic material derived from complete microbial communities harvested from natural environments. For example, the gut microbiota complements our own genome with metabolic functions that affects human metabolism and may thus play an important role in health and disease.
Type 2 diabetes (T2D) is a metabolic disorder characterized by hyperglycemia and defects in insulin secretion and action. T2D is on the rise worldwide and an estimated 350 million people will be affected by 2030. This chronic disease is associated with multiple metabolic and cardiovascular comorbidities, and increased mortality from cardiovascular complications. Equally alarming is the fact that about half of all patients with T2D are newly detected, and many of them have cardiovascular complications at the time of diagnosis. Long before diabetes develops, impaired glucose tolerance (IGT) and other metabolic defects may appear. Since pharmacological and lifestyle interventions can reduce or postpone diabetes, especially in subjects with IGT, early detection of individuals at risk of T2D, for example individuals with IGT, is important for prevention of T2D and for reducing the costs of medical care.
T2D is a result of complex gene-environment interactions, and several risk factors have been identified, including age, family history, diet, sedentary lifestyle, and obesity. Statistical models that combine known risk factors for T2D can reasonably identify IGT and T2D individuals. However, these studies also indicate that genetic markers contribute little to the models, while socio-demographic and environmental factors have greater influence so there is a need for more accurate tools for prediction of future T2D risk.